1. Techinical Field
This invention relates generally to apparatus for adjustment of spark plug electrode gaps and more particularly to combination tools arranged to set the gap on aviation or industrial spark plugs.
Spark plug removal for cleaning or replacement in aircraft engines is a mandatory operation during routine maintenance or required overhaul. It is quite common to find that regapping is required after cleaning or for initial setting of a new plug. Such gaps may be either large or small, necessitating a tool for both quick opening or closure of said gap.
2. Background Art
Development of spark plug gapping tools has usually been directed toward either plier or lever type instruments. This latter type has long been utilized in bending electrode on automotive spark plugs, with side edge slotted designs being most prevalent. In use, an "L" shaped stud or wire electrode is bent by levering about its own attachment point. A variation of this approach, in which levering is against either the other electrodes or against the plug body itself is best illustrated by Rabezzana in U.S. Pat. No. 1,812,496. Here, a cam-like, "C" shpaed open end wrench is rotated in the annular region about the center electrode. Closure is effected by bending the side electrode against the center electrode, and opening is caused by levering the side electrode against the plug housing. In the field of aircarft spark plugs however, side annular spaced electrodes are also frequently used. Two or three stud electrodes are equally spaced about a center electrode. Care must be taken to bend these side electrodes without overstress, and it is not desirable to touch and possibly scratch the center electrode.
A plier type tool can be used to close a gap by bending one side electrode against another, but a problem exists in obtaining equal spacing. Special pliers for aircraft spark plug gap opening are illustrated by Pentland, in U.S. Pat. No. 2,581,439. A tool is therein described which grips the side electrode and opens the gap by fulcruming the pliers against the electrode shell. Its use, however, in gap closure is more dangerous relative to the ability to touch the center electrode, and such use is not recommended.
Although wire type plugs are more amenable to single slot type gap closures, the mechanic is forced to carry on array of special instruments. A need exists therefore for a single combined instrument which is adapted for use across the variety of aircraft spark plugs encountered by the aviation mechanic.